Turkey's bombarding of U.S.-backed Kurdish forces in Syria is threatening to overshadow U.S. Vice President Joe Biden’s visit to Ankara on Wednesday.

Turkish artillery also has been shelling Islamic State forces in the Syrian border town of Jarabulus since Monday. Jarabulus is a key supply route for IS, the last remaining town under its control on the Turkish border. The bombardment follows the Turkish foreign minister’s promise to eradicate IS from the border.

"We will cleanse the Syrian border of Daesh’s presence," Mevlut Cavusoglu said. Daesh is another name for Islamic State.

The foreign minister made the commitment following Saturday's suicide bombing of a Kurdish wedding in the Turkish city of Gaziantep. Initial reports blamed IS.

Turkey has been massing tanks on the Syrian border to offer support ahead of a widely predicted offensive by the Turkish-backed Free Syrian Army to capture Jarabulus.

But Turkish artillery is also targeting Syrian Kurdish forces of the YPG, in an action seen as seeking to thwart the rebel group's attempts to seize Jarabulus. The YPG makes up the vast majority of the Syrian Democratic Forces, which, backed by the U.S. military, have inflicted a series of crushing defeats on IS.

Link to PPK

Ankara, however, accuses the Syrian Kurds of being terrorists linked to Kurdish PPK rebels. International relations expert Soli Ozel of Istanbul’s Kadir Has University said differences between Ankara and Washington over the Syrian Kurdish political party, the PYD, and its military wing, the YPG, could dog Biden’s visit.

"I haven’t seen anything to suggest that the Americans have stopped helping Turkey on the PKK," Ozel said. "What Turkey is saying [is], "Well, look, the PYD is a Syrian extension of the PKK, so you should also not help them.' But that argument has been rejected by the Americans time and again, and very consistently. So can they continue this game? I have no idea. I think this issue is going to be one of the major issues when Biden comes."

Ankara accuses the PYD of seeking to carve out an independent state on Turkey’s border, which it fears will incite Turkey’s own restive Kurdish minority. With U.S. and U.K. special forces believed to be in the midst of the Syrian Kurdish forces as advisers, Washington will most likely be seeking to defuse rising tensions.

Biden’s visit comes as Ankara is also reaching out to Tehran and Moscow. Turkish political columnist Semih Idiz of the Al Monitor website said Turkish diplomacy is geared only toward thwarting Kurdish aspirations.

"If Turkish relations with Washington and Moscow and Tehran improve and are reinforced ... by Iran’s dislike of a Kurdish entity in northern Syria also, then the influence of the Kurds will start waning," Idiz said.

During his planned meeting with Turkish President Recep Tayyip Erdogan, Biden is widely predicted to face intense pressure for Washington to abandon the Syrian Kurdish forces. Observers claim such a move is unlikely, given that the Syrian Kurds are viewed as the most effective force fighting the jihadists, especially with the key battle looming to capture Raqqa, Islamic State’s self-declared capital.